1. Field of the Invention
The present invention relates to an improvement in an exhaust system for a motorcycle.
2. Background of the Invention
A wide variety of layout configurations have been proposed for the muffler and exhaust pipe in an exhaust system of a motorcycle. An example of an exhaust system configuration is disclosed in Japanese Patent Laid-open No. 2003-74337 (FIGS. 3 and 4).
FIG. 3 of Japanese Patent Laid-open No. 2003-74337 shows an exhaust pipe 18. The exhaust pipe 18 is composed of an exhaust pipe front portion 61, a right side connecting pipe 62 extending rearwards from the exhaust pipe front portion 61 and connected to a muffler 23 disposed on the right side, and a coupling pipe 63 for connecting the right side connecting pipe 62 with a muffler 22 disposed on the left side (refer to paragraph [0015] of Japanese Patent Laid-open No. 2003-74337). The coupling pipe 63 extends crosswise directly above the rear wheel, as indicated by imaginary lines.
FIG. 4 of Japanese Patent Laid-open No. 2003-74337 is a side view of the exhaust system of FIG. 3, in which the coupling pipe 63 passes below tandem seat 43 at a position which is spaced a vertical distance C from the bottom of a sunken portion 43c of a tandem seat 43. Therefore, the allowable margin through which the rear wheel 21 is permitted to rise is determined by the height of the underside of the coupling pipe 63, as indicated by an imaginary line 82.
Meanwhile, in motorcycles such as off-road vehicles and trial vehicles, the suspension of rear wheel is required to accommodate a large degree of contraction/expansion during navigation of rugged operation terrain. Therefore, the exhaust pipe structure shown in Japanese Patent Laid-open No. 2003-74337 is not suitable for these types of motorcycles, since the allowable margin through which the rear wheel 21 is permitted to rise is too small.
However, in connection with motorcycles equipped with left and right mufflers, there is a keen demand for an exhaust pipe structure which enables an increase in the allowable margin through which the rear wheel is permitted to rise.